Some of the starter kits are mixed with loam, and completely dry loam (ie - used as a 'decorative' substrate in the basin) will cover your ants quite easily.
I'd advise you to go to your nearest pet-shop that deals with reptiles/aquariums, and either get some coral-white-sand, or for reptiles you could get a small bag of white "calci-sand", and just carefully spoon it in (table-spoon!) to the basin, being careful to work around the ants there (don't want to frighten the poor buggers with a spoonful of sand!

).
Yeah, I talk with such experience don't I... *ahem* - I made the same mistake with my new colony. I thought I was just buying a 1 KG bag of white sand from AntStore, after noticing lots of my new Myrmica workers turning white (and wondering if they were going ninja disguised as rocks

), I realised it was loam (and double checking my order/online, I had indeed ordered a pre-mixed bag of loam & white sand). So I nipped out to my nearest aquarium, covered the loam/sand with about 1CM of "calci-sand" (quite expensive but the only bags of more ordinary white sand they sold were in huge 25kg bags, which would have been much more expensive even if it was a whole lot cheaper 'per kilo'), and they are fine now, no longer getting covered, and they seem to be able to walk around on it much easier too.